The present invention relates to the observation or inspection of a fine object, and more particularly to a scanning electron microscope (hereinafter referred to as "SEM") which can readily change the field of view for observing a fine object.
In a case where the field of view of an SEM for observing a specimen is changed, two methods can be used. In one of the methods, the point of incidence of an electron beam is changed by adjusting an electron lens. In the other method, a specimen table loaded with the specimen is moved. The former method has advantages that it is not required to move a specimen table but the field of view is changed by a simple operation. However, the field of view is changed only in a narrow range, and moreover the positional accuracy of the point of incident of the electron beam is not satisfactory. Thus, the latter method is actually used. In the latter method, the specimen table is moved by the combination of the horizontal movement, rotation and tilt of the specimen table, and these operations of the specimen table are coupled directly with the mechanical movement of controls which are operated by an operator. In a case where the specimen table has a simple structure, that portion of a specimen which is now observed, may go out of the field of view only by tilting the specimen table a little. In order to solve the above problem and to make easy the observation of a fine object, a specimen table provided with a sophisticated movable part has been proposed in, for example, an article entitled "Five-Degrees-of-Freedom Stage for a Scanning Electron-Beam Microscope" (IBM Technical Disclosure Bulletin, Vol. 26, No. 3A, pages 1173 and 1174, 1983). Further, a system for testing a semiconductor device has been developed, in which a specimen table is automatically moved so that measured points are successively irradiated with an electron beam, or is automatically moved to a position which is specified on a design drawing, and accurate positioning is carried out on the basis of video information. This system is described in, for example, an article entitled "EB Test System linked with CAD Database" by F. Komatsu et al. in the Material of the 97th Meeting of the 132nd Committee on the Application of Charged Particle Beam to Industries, pages 63 to 68 (Japan Society for Promotion of Science.
According to the specimen table described in the former article, the mechanical operation of specimen table is independent of the magnification of the SEM, and thus the moving speed of the field of view varies with the magnification. Further, the mechanical operation of specimen table is limited by the mechanical structure thereof, and moreover, the operation accuracy of the specimen table is reduced by mechanical wear thereof. While the system described in the latter article can be used only for a case where an object to be observed is previously determined.